1. Field of the Invention
The present invention relates to a regenerative refrigerator that stores the cold generated by Simon expansion of a high-pressure refrigerant gas supplied from a compressor.
2. Description of the Related Art
An exemplary regenerative refrigerator generates the cold by expanding a helium gas in an expansion chamber. The cold of the helium gas generated in the expansion chamber is stored in the regenerator and is transferred to a cooling stage, which reaches a desired cryogenic temperature and cools a cooling object connected to the cooling stage.
A regenerator material is used in a regenerator. The specific heat of a non-magnetic regenerator material such as copper is smaller than that of the refrigerant helium gas in a cryogenic temperature region of, for example, 10 K or below. Therefore, a magnetic regenerator material, which has a relatively large specific heat in a cryogenic temperature region, is used in a regenerator in that temperature region.